Compressive forming



Nov. 22, 1966 R. M. COGAN 3,286,493

COMPRESSIVE FORMING Filed Feb. 5, 1964 2 Sheets-Sheet 2 E5 BY 56% United States Patent 3,286,498 COMPRESSIVE FORMING Richard Maurice Cogan, Hamilton, Mass., assignor to General Electric Company, a corporation of New York Filed Feb. 3, 1964, Ser. No. 341,909 7 Claims. (Cl. 7261) This invention relates to the forming of articles through the use of compressive forces, and more particularly to a method for use in the compressive forming of hollow metallic articles. This application is a continuation-inpart of application Serial No. 245,734, filed December 19, 1962, and assigned to the assignee of the present invention.

Many types of extrusion processes useful with relatively ductile materials are well known in the metal working art. Typical of the patented art with regard to methods of making hollow articles are such United States patents as 2,027,285-Parker, 2,138,199Wendel and 2,243,809 -Wendel. One example of hydraulic die forming using aliquid filler within the hollow portion of the-workpiece and a readily retractable guiding material such as retractable plugs is shown in United States Patent 2,138,199. The hollow workpiece is deformed by applying directly to the workpiece a single force which exceeds that which is required to plastically deform the material, various guiding means being used internally or externally to guide the flow of the moving metal.

The newly developed strong nickel or cobalt base super alloys or the new refractory metals alloys having extremely high strength but relatively low ductility resist forming methods such as described in the prior art. Such known methods, if suflicient force is applied to move the metal, result in brittle fractures, cracks and generally defective articles. The extrusion forming of such newer materials by such known methods can be safely accomplished only for a small percentage extrusion in each operation before some additional treatmentis required to avoid cracking of fracture. Thus presently used articles of super alloys of the nickel base or cobalt base type or of the refractory metals alloys are not fully extruded as a practical manufacturing method.

Experiments in the field of fracturing of metals as well as the above identified co-pending patent application of which this is a continuation-in-part has shown that the application of external pressures to a metallic material during working results in a great increase in ductility. A typical example of such published information is Studies in Large Plastic Flow and Fracture by P. W. Bridgman in the Metallurgy and Metallurgical Series published by McGraw-Hill Book Company, Inc. in 1952.

It is a principal object of this invention to provide an improved method for the compressive forming of a hollow workpiece into an article through the controlled and coordinated application of both external and internal pressure,

Another object is to provide an improved method for the compressive forming of hollow circular workpieces of difiicult to work materials by the controlled application of pressure to the outer portion of the workpiece coordinated with the controlled application of pressure to the hollow internal portion of the workpiece.

These and other objects and advantages will be more readily recognized from the following detailed description and the drawing in which:

FIGS. 1, 2 and 3 are sectional, partially schematic views of the sequential steps in one form of the method of the present invention; 1

FIGS. 4 and 5 are sectional, partially schematic views of two sequential steps of another form of the method of the present invention;

3,286,498 Patented Nov. 22, lgiifi FIGS. 6, 7 and 8 are sectional, partially schematic views of sequential steps in still another form of the present invention.

Briefly, the present invention provides, in a method of compressive forming an article from a workpiece having a hollow core, the steps of placing the workpiece under compression with a first force which is less than that required to plastically deform the material of the work: piece, and applying to walls of the hollow core a second force which when added to the first force exceeds that force required to plastically deform the material of the workpiece.

Although the more difficult to work super alloys and refractory metals and metal alloys can be made into various article shapes such as by precision casting or by powder metallurgy processes, the mechanical properties of such articles fail to meet some of the more stringent requirements as those required for hollowcomponents designed for use in improved propulsion apparatus such as jet engines. Any working or extrusion of such components produced by casting or powder metallurgy techniques requires either the use of extremely high pressure equipment which, though known, is not presently used in production,or requires the addition of heat to lower the material flow strength. Even widely used materials as A.I.S.I. type 4340 steel requires excessively high punch capabilities in order to form components under hydrostatic pressure. Y

The present invention provides a method for producing fiber elongation of the inside diameter of hollow workpiece members up to as much as about 250% and height reductions of greater than 65%, without the addition of heat. This is accomplished through the controlled and coordinated application of a first compressive force to the workpiece material less than that materials compressive yield strength and a second force applied to the internal surface of the hollow workpiece which, when added to the first force, exceeds the compressive yield strength of the workpiece material. Compressive yield strength, as used herein, means the maximum stress that a material subjected to compression can withstand without a predefined amount of plastic deformation.

This invention will be more fully understood by reference to the drawing. In the embodiment of FIGS. 1-3, hollow article 22 of FIG. 3, which can be a hollow ring, is produced from hollow workpiece 20 of FIG. 1. According to one form of the invention, the workpiece 20 having a hollow core or matrix chamber 24 is placed between two members of a press 26 and 28. The details of the press are not shown because a variety of such presses are well known in the art and some ultra-high pressure equipment has been reported in the literature. One publication appeared in Mechanical Engineering magazine published by the American Society of Mechanical Engineers, October, 1961, at pages 37-43. The present invention contemplates the use of such equipment to apply the forces represented schematically by the various arrows in the drawing.

As shown in FIG. 1, a matrix 30, which is preferably a solid material such as a metal for ease of handling, is then introduced into hollow core 24 by ram 32 as a means to transmit the application of a force uniformly to the internal walls 20a of the hollow core 24. Although this particular operation of adding matrix to the core is shown in the drawing, it should be understood that the workpiece after the introduction of the matrix comprises a composite billet with a matrix core and a .high strength outer rim. Thus the composite billet possibly with additional matrix 30 extending from the billet can be made by a variety of methods prior to its being introduced between members 26 and 28 of the press.

At the beginning of the method of the present invention, a first force represented schematically by arrows 34, is applied to workpiece 20 through members 26 and 28 of the press. This first force is less than the workpiece materials compressive yield strength. That is, it is less than that required to plastically deform the material of the workpiece and places the workpiece material under compression. A second force 36 is then transmitted from punch 32 through matrix 30 to the internal walls 20a of hollow core 24 of workpiece 20. The second force is greater than the compressive yield strength of the matrix material and, when added with the first force 34, at least exceeds that strength required to cause plastic deformation of the material of the workpiece 20, the compressive yield strength of the workpiece material. With these combinations of forces, workpiece 20 is extruded radially outwardly, being guided by the shape of surfaces 26a and 28a which can be the surface of dies and which can be complex shaped sunfaces. The combination of the first compressive force 34 and the second compressive force 36 as applied to the workpiece, maintains the workpiece in -a ductile condition to allow unexpectedly large percentages of fiber elongation in extrusion while preventing the cracking or formation of defects in the final workpiece 22 shown in FIG. 3.

In FIGS. 4 and 5, where like numbers refer to the like members as in FIGS. 1-3, a form of the present invention is represented wherein the second force is applied to matrix 30 from a plurality of directions such as from counter opposed punches.

EXAMPLE I In one example of the practice of the method of the present invention, a solid billet of A.I.S.I. type 4340 steel was heat treated to a hardness of 42 Rockwell C and machined to the ring shape configuration shown as workpiece 20 in FIGS. 1 and 2. The billet dimensions were 0.500" height, 0.75" outside diameter and 0.375" diameter of the hollow core. This ring shaped billet was clamped between two die faces such as 26a and 28a of FIG. 2. A first force or load just below the compressive yield strength of A.I.S.I. 4340 steel of 150,000 pounds per square inch was applied to the ring shaped billet. A low strength matrix of lead was then pressed into the hollow core of the billet by a ram such as 32 in the drawing and a second force of about 20,000 p.s.i. was applied through the ram and matrix material to the walls of the hollow core portion of the ring shaped billet. The billet was expanded in a ductile manner until the fiber elongation of the inside diameter was elongated to 247% with a reduction in height of 66.5% to form the ring member shown as 22 in FIG. 3. At the conclusion of the expansion, the billet dimensions were 0.168" height, 2.10" outside diameter and 1.30" diameter of the hollow core.

In this example, the workpiece height was decreased as the workpiece diameter increased. In order to maintain friction at a minimum, the wall thickness was held constant as the workpiece was formed. This was done in order to establish a relationship between the workpiece height and diameter which was programmed by controlling the feed of the matrix into the hollow center of the workpiece as the workpiece was reduced in height. This also allowed for maintaining the maximum diameter wall thickness ratio throughout the forming operation.

EXAMPLE II A hollow billet of the type described in Example I with a lead matrix core was placed between two dies of a press and upset in a conventional manner by applying the same pressure to the soft matrix core as was applied to the material of the workpiece. Of necessity the force applied in this example exceeded the compressive yield strength of the material of the workpiece, that is, that force required to plastically deform that material. After 40% elongation of the fibers of the inside diameter, the billet fractured.

In tests of the type conducted in Example I on similar alloys, it has been found that in the practice of the present invention with a. ratio of workpiece or billet height to wall thickness of greater than 5, the expansion does not take place uniformly over its height. A uniform ring billet tends to form a hollow member shaped similar to the frustrum of a hollow cone.

EXAMPLE III The procedure of Example I was repeated on a billet shaped as that in Example I having a height of 0.500", an outside diameter of 2.00" and a diameter of the hollow core of 0.75". The material was a molybdenum basealloy having a composition of 0.5 weight percent titanium with the balance molybdenum. The first force applied through the molybdenum alloy billet was just below its compressive yield strength of about 97,000 p.s.i. and the second force applied though the matrix to the walls of the hollow core portion of the billet was 22,000 p.s.i. A reduction in height of 33% was achieved along with elongation of the inner fibers in excess of 20%. Conventional upsetting of a hollow billet with a soft matrix core of this molybdenum base alloy fractures on the inside diameter after an elongation of less than 2% and generally ahnost immediately upon any elongation of the fibers.

The matrix material which is preferred to be used at the present time because of limitations in pressure equipment available, generally has a compressive yield strength of less than that of the workpiece material. However, it will be understood from the unusual and unexpectedly great differences in elongation between hollow workpieces filled with a matrix and upset by conventional means and the elongation achieved in the practice of the present invention that the matrix material introduced into the hollow core can be the same as or even have a higher compressive yield strength than that of the workpiece material. An important feature of the method of the present invention is the relative magnitudes of the first and second forces as and where applied to the workpiece in order to allow the significantly greater percent expansion of the workpiece in a single upsetting or extrusion process without the introduction of intermediate heat treatments and the like.

Furthermore, it should be understood that although the shape of the workpiece shown in connection with the drawing and the examples is a regular hollow circular billet, it is to be understood that the practice of the method of the present invention can be applied to other hollow geometric shapes of substantially uniform wall thickness so that the force applied from Within the workpiece can be appropriately transmitted to all portions of the workpiece material. In addition, it is contemplated that workpiece members of irregular shapes such as shown in FIG. 9 can be compressively formed according to the method of the present invention provided the mating surfaces of members such as dies which contact the external top and bottom surfaces of the workpiece direct the first force to place the workpiece material in compression with a force below its compressive yield strength.

As the parent application to this continution-in-part has shown, unusual results can be achieved in the compressive forming of articles in a die cavity by extruding the workpiece against a matrix in the die cavity, which matrix is, in turn, forced from the die cavity by the expanding workpiece. As shown in FIGS. 6, 7 and 8, that feature of the parent invention can be combined with the present invention to obtain additionally improved results, particularly with regard to the outer surface of the expanding gcrkpiece in contact with the matrix extruded from the In FIGS. 6, 7 and 8, workpiece is placed in the cavity formed by top and bottom die members 40 and 42, respectively, along with matrix which fills the hollow core portion of workpiece .20 and matrix 30a which fills the die chamber external to the workpiece. Matrix 300: can be placed in the die cavity as a hollow core member such as a ring member, the matrix hollow core having dimensions substantially the same .as the outer dimensions of the workpiece. During the practice of this form of the process, similar to that described in connection with FIGS. 1, 2 and 3, a first force 34 is "applied to the workpiece through die members and 42 such as from a press. This first force is less than that required to plastically deform the material of the workpiece. A second force 36 is applied through the matrix material 30 to the walls of the hollow core portion of the workpiece. Force 35 is greater than that which is required to plastically deform the material of the matrix and when added with first force 34 exceeds that force required to plastically deform the material of the workpiece, i.e., exceeds the compressive yield strength of the material of the workpiece. Thus workpiece 20 is extruded farther into the die cavity at the same time forcing matrix material 30a through orifices 44 at a rate which controls a reaction force of the matrix material 39a at the interface between that portion of the matrix and the external walls of workpiece .20 to inhibit cracking of the workpiece as is more fully described in the parent application.

Although the present application has been described in connection with specific examples, those skilled in the arts involved will understand the modifications and variations of which the invention is capable within its broad scope.

What is claimed is:

1. In a method of compressive forming an article from a workpiece having a hollow core, the steps of (a) placing all of the material of the workpiece under compression with a first force which is less than that required to plastically deform the material of the workpiece; and

(b) applying to internal walls of the workpiece hollow core a second force;

(c) the sum of the first and second forces exceeding that force required to pl'astically deform the material of the workpiece.

2. In a method of compressive forming an article from a workpiece having a hollow core and having a ratio of workpiece height to wall thickness of 5 or less, the steps of:

(a) placing all of the material of the workpiece under compression with a first force which is less than that required to plastically deform the mate-rial of the workpiece; and

(b) applying to internal walls of the workpiece hollow core a second force; which (c) the sum of the first and second forces exceeding that force required to plastically deform the material of the workpiece.

3. In a method of compressive forming an article from a workpiece having a hollow core, the steps of:

(a) placing all of the material of the workpiece under compression with a first force which is less than that required to plastically deform the material of the workpiece;

(b) introducing a matrix material into the workpiece hollow core; and

(c) applying to internal walls of the workpiece hollow core through the matrix material a second force which exceeds the compressive yield strength of the matrix material the second force moving all of the material of the workpiece radially outwardly from the axis of the hollow core;

(d) the sum of the first and second forces exceeding that force required to plastically deform the material of the workpiece.

4. In a method of compressive forming an article from a workpiece having a hollow core, the steps of:

(a) placing all of the material of the workpiece under compression with a first force which is less than that required to plastically deform the material of the workpiece;

(b) introducing into the workpiece hollow core a matrix material having a compressive yield strength less than that of the workpiece material; and

(c) applying to internal walls of the workpiece hollow core through the matrix material a second force which exceeds the compressive yield strength of the matrix material the second force moving all of the material of the workpiece radially outwardly from the axis of the hollow core;

(d) the sum of the first and second forces exceeding that force required to plastically deform the material of the workpiece.

5. In a method of compressive forming a hollow circular article from a hollow circular workpiece having a hollow core the steps of:

(a) placing all of the material of the workpiece under compression with a first force which is less than that required to plastically deform the material of the workpiece;

(b) introducing into the workpiece hollow core a matrix material having a compressive yield strength less than that of the workpiece material; and

(c) applying to internal walls of the workpiece hollow core through the matrix material a second force which exceeds the compressive yield strength of the matrix material the second force moving all of the material of the workpiece radially. outwardly from the axis of the hollow core;

(d) the sum of the first and second forces exceeding that force required to plastically deform the material of the workpiece.

6. In a method of compressive forming a hollow article in a die cavity from a workpiece having a hollow core, the steps of:

(a) placing a matrix material in the die cavity;

(b) placing the workpiece in the die cavity such that the outer periphery of the workpiece not contacted by the die cavity is surrounded by matrix material, the workpiece and matrix material together filling the die cavity except for the workpiece hollow core;

(0) placing the workpiece under compression with a first force which is less than that required to plastically deform the material of the workpiece; and

(d) applying to walls of the workpiece hollow core a second force;

(e) the sum of the first and second forces exceeding that force required to plastically deform the material of the workpiece, the deforming workpiece displacing the matrix in the die cavity.

7. Ina method of compressive forming a hollow article in a die cavity from a workpiece having a hollow core the steps of:

(a) placing a first matrix material in the die cavity;

(b) placing the workpiece in the die cavity such that the outer periphery of the workpiece not contacted by the die cavity is surrounded by the first matrix material, the workpiece an-d first matrix material together filling the die cavity except for the workpiece hollow core;

(c) placing the workpiece under compression with a first force which is less than that required to plastically deform the material of the workpiece;

(d) introducing a second matrix material into the workpiece hollow core; and

(e) applying to walls of the workpiece hollow core through the second matrix material a second force which exceeds the compressive yield strength of the matrix material;

7 (f) the sum of the first and second forces exceeding that force required to plastically deform the mate rial of the workpiece, the deforming workpiece displacing the first matrix material from the die cavity.

References Cited by the Examiner UNITED STATES PATENTS 436,676 9/1890 Smith 72-343 601,825 4/1898 Conners 7262 1,613,595 1/1927 Abel 72-353 1,710,776 4/ 1929 Langenberg 7262 8 2,027,285 1/1936 Parker 29157 2,138,199 11/1938 Wendel 72353 2,168,641 8/1939 Arbogast 72-654 2,243,809 5/ 1941 Wendel 29157 OTHER REFERENCES Bridgman, P. W., Studies in Large Plastic Flow and Fracture, McGraw-Hill Book C0., Inc., 1952, pp. 1-2.

0 CHARLES W. LANHAM, Primary Examiner.

L. A. LARSON, Assistant Examiner. 

1. IN A METHOD OF COMPRESSIVE FORMING AN ARTICLE FROM A WORKPIECE HAVING A HOLLOW CORE, THE STEPS OF: (A) PLACING ALL OF THE MATERIAL OF THE WORKPIECE UNDER COMPRESSION WITH A FIRST FORCE WHICH IS LESS THAN THAT REQUIRED TO PLASTICALLY DEFORM THE MATERIAL OF THE WORKPIECE; AND (B) APPLYING TO INTERNAL WALLS OF THE WORKPIECE HOLLOW CORE A SECOND FORCE; (C) THE SUM OF THE FIRST AND SECOND FORCES EXCEEDING THAT FORCE REQUIRED TO PLASTICALLY DEFORM THE MATERIAL OF THE WORKPIECE. 